This is my average guide for Pokemon Snap. It tells you what pokemon are in each level, and ways to find hard pokemon, and get cool shots. This guide is outdated; I haven't played in so long, so if you need help you'll have to try gamefaqs.com.
Level 1: Beach
You already have this level unlocked. You find a lot of basic pokemon here. At the beginning of the level you can get a really awesome picture of Pidgey, with two other Pidgey's in the background. You can also lure Pikachu with Apples to the surf Board. That really gives professor Oak a big w00t.
Level 2: Tunnel
To unlock this, you must take pictures of 6 different pokemon in the first level. Pikachu is the only pokemon that isn't new here. You can get him to ride Electrode at the beginning of the level. Also, throwing apples at electrode will make him explode! You can also meet Zapdos here. Just make his egg hatch. Also, you can lure the three Magnemites together to make a Magneton. Use apples.
Level 3: Volcano
You need to hit the Electorde at the end of the 2nd level to unlock this level. All the pokemon here are fire type. Also, there are a lot of tricks you can do! You can get Moltres. Just throw an apple at his egg. His egg is hard to miss! At the end of the level, knock the charmeleon into the lava to make him evolve. Make sure you snap him before he evolves.
Level 4: River
To unlock this course, you need to have atleast 22 pictures of different pokemon. Most pokemon here are either water, or grass type. Throwing apples may get Butterfree to come out. Otherwise, there is no real strategy here. This level is easy.
Level 5: Cave
To unlock this course you must go to the River course. Near the end of the River course, there's a red switch at the right side and a weird rock moving around on the wall. Hit the rock with a pester ball to turn it into Porygon and hit the switch. You can find Articuno here. Hit all the Jynx's to make them break his egg. Near the end of the level you can find some Jigglypuff's getting picked on by another pokemon. If you help the three Jigglypuff's than at the end of the level, one will sing, and the other two will dance. What a shot that could be.
Level 6: Valley
To unlock this course you must take pictures of 40 different types of pokemon. You will find pokemon on the rocks, and in the river in this level. If you toss 4 Pester Balls into the whirlpool Dragonite will come out. Otherwise the rest of the pokemon are simple.
Beach: This sign looks like a crab made out of rocks. You'll find it on the left near the start of the level.
Tunnel: This sign is a shadow cast on a wall, and it's found before the magnemite nearthe end of the level. In order to see it though you must first release Zapdos from its egg earlier on in the stage.
Volcano: This sign looks like purple smoke, and you'll find it on the left near the start of the level. Throw a pester ball or two into the volcano on the left to get this sign to appear.
River: This sign looks like a large rock formation and is found above the Vileplume near the beginning of the level.
Cave: This sign looks like formation of four shiny crystals and it's found midway through the level. Look left once you see the first Koffing and Jigglypuff, you shouldn't miss it.
Valley: Right at the start of the level you will see three mounds in the distance. This is exactly what you are looking for.
Level 7: Rainbow Cloud
To unlock this, you must have taken pictures of all 6 pokemon signs. In this level, there is only one pokemon: Mew. He will be protected from getting his picture taken. You need to hit him with an apple, or Pester Ball a few times. He than loses his bubble. He will be running to get to his bubble so you wouldn't be able to see his face. You can sometimes intrest him with an Apple to get him to turn around.